1. Field of the Invention
The invention relates to a conveying unit having a pump, which has a pump wall, and having a filter element which is to be fastened to the pump wall in the region of an inlet duct.
2. Description of the Related Art
Conveying units of this type are, for example, used to a great extent in today""s motor vehicle in a fuel tank for the conveying of fuel, and are therefore known. The conveying unit generally forms a preassemblable unit together with an electric motor provided for driving the pump. In this connection, the inlet duct has a connecting branch which protrudes from the pump wall and onto which a connecting piece of the filter element is plugged (DE 44 31 738 A1). The connecting piece is then secured to the connecting branch by means of a pipe clip.
A disadvantage in the case of the known conveying unit is the fact that the pump wall is a component which can be difficult to manufacture because of the protruding connecting branch. The conveying unit becomes very cost-intensive as a result. Furthermore, because of the connecting branch the filter element is at a very great distance from the pump wall, and the conveying unit is hence a very bulky component.
U.S. Pat. No. 5,411,376 discloses a conveying unit which has a large axial extent and instead of a connecting branch has an inlet covering which is like a connecting branch and in which a filter element is arranged. A covering of this type means that the pump bottom can be designed more simply but because of the additional component the outlay on installation for this conveying unit is increased.
The invention is based on the problem of designing a conveying unit of the type mentioned at the beginning in such a manner that it can be produced particularly cost-effectively and has the smallest possible dimensions.
According to the invention, this problem is solved by the filter elements being prestressed against the pump wall.
By means of this design, the filter element bears directly against the pump wall which has the inlet duct. A connecting branch for the fastening of the filter element, as in the case of the known conveying unit, is therefore no longer required. As a result, the conveying unit according to the invention manufactured in one piece with a housing of the conveying unit or the pump, and has a flanged border which bears against the edge of the filter element. A flanged border of this type is in any case generally required in order to secure individual components of the pump to one another. The manufacturing costs for the conveying unit according to the invention are thereby kept particularly low. Furthermore, the filter element is thereby fastened particularly reliably to the pump even when the motor vehicle is vibrating strongly.
To further reduce the production costs for the conveying unit according to the invention it helps if the pump wall is produced from ceramic by sintering. Since, because of the invention, the pump wall can be configured such that it is flat, a sinter form which is required for producing the pump wall is constructed in a particularly simple manner and can easily be removed from the mold axially. Furthermore, ceramics used in the sintering technique have a particularly high surface hardness, a hard compressive strength and good corrosion resistance, so that the conveying unit has particularly high durability. Suitable ceramics include, for example, silicon carbide or oxide ceramic. The particularly high durability of the conveying unit according to the invention is, in particular, necessary if the conveying unit is provided for use in a fuel tank which is produced cost-effectively in a blowing process. In this connection, after the blowing procedure, the conveying unit is contained in the fuel tank and can no longer be removed. A further advantage of this design resides in the fact that noises which are produced within the pump by the pump wall, which is manufactured from ceramics, are absorbed particularly well.